Hide PII from external reviewers, along with private reviews

[wes-otf]

Fixes #3240. Adds HIDE_IDENTITY_FROM_REVIEWERSconfig option to hide the identities of staff & applicants from external reviewers. This also hides reviews that don't have visibility set to reviewer from the sidebar as that seemed ore intuitive.

There is also a fix here for the Updated field of the application where the original author will always be specified as the application editor even if someone else updated it. This is an edge case but will be helpful as we implement things like #3919.

Test Steps

• [ ] As an applicant, submit a new application to a fund that has external review
• [ ] As staff, assign an external reviewer to the application & move the it into the external review phase.
• [ ] While still staff, add a review & set the visibility to private
• [ ] As the assigned external reviewer, ensure...
  • [ ] the applicant's name & other PII are not present anywhere on the submission
  • [ ] the staff review that was marked private is not visible in the Reviews & assignees sidebar
• [ ] As staff, edit the previous review & set visibility to reviewers
• [ ] As the reviewer, ensure the edited review is visible in the sidebar

[wes-otf]

rebased onto #3948 to use those features so some of the diff may be duplicated - code changes in this PR can be found here

[wes-otf]

This is ready for review. I was going to add some unit tests for the view_partials, does anyone have previous examples of this they could toss my way so I could have an example for the review sidebar? @theskumar?